Lab 12 Human Genetics

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Dec 6, 2023

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Note: All your answers to questions must be in Red or other color (not including blue) for easier grading. Points will be deducted if you do not distinguish your answers. Lab 12. Patterns of Inheritance Objectives:  Determine the genotype by observation of individuals with given traits and their relatives.  Determine inheritance involving autosomal dominant, autosomal recessive and x-linked recessive alleles.  Determine inheritance involving multiple allele inheritance and use blood type to help determine paternity.  Describe a normal human karyotype and discuss the various abnormalities that can be detected using this technique  Using a karyotype analyze a patient’s chromosomes to determine if inheritance is normal or a chromosomal anomaly is present.  Analyze a pedigree to determine the pattern of inheritance for an allele – autosomal dominant, autosomal recessive or x-linked recessive.  Create a pedigree to determine the probability of inheritance of a particular phenotype when given generational information only. Vocabulary:  Genotype  Phenotype  Autosomal dominant  Autosomal recessive  Heterozygous  Homozygous  Probability  X-linked recessive  X-linked dominant  Multiple alleles  Codominance  Karyotype  Pedigree

Introduction: Just like in pea plants, Mendel’s laws of inheritance also apply to humans. Humans inherit 46 chromosomes that occur in 23 pairs, 22 pairs of autosomes and one pair of sex chromosomes (either XX or XY). This means that all autosomal genes exist in two forms, called alleles. These alleles may be genetically identical, called homozygous (AA or aa) or they may be genetically different (Aa or aA). The fact that one allele may be dominant over the other determines what phenotype is exhibited. Dominant alleles are represented by capital letters (A) and recessive are represented by lower case (a). Thus, you can have homozygous dominant (AA) or homozygous recessive (aa) and of course heterozygous (Aa). When a gene follows Mendel’s laws of inheritance (MOST genes do not), it is easy to predict the ratios of potential offspring using Punnett squares, or for example to determine the genotypes of parents from the genotype or phenotype of the offspring. In this section of the lab, we will practice determining the genotype given information about the gene and inheritance of it. Part 1: Determining Genotype Table 1 shows several autosomal human traits and indicates which is dominant and which is recessive. Fill out Table 1 and answer the following questions. (If you are not sure what the trait looks like, refer to Figure 1-5 , or you can do a quick internet search for an image of that trait.) Figure 1: Left – Widow's peak (dominant) versus Right– straight hairline (recessive). Figure 2: Left – No Hitchhiker’s thumb (dominant) versus Right– Hitchhiker’s thumb (recessive).

Figure 3: Right – attached earlobes (recessive) versus Left– unattached earlobes (dominant). Figure 4: Left– freckles (dominant) versus Right– no freckles (recessive). Figure 5: Left– dimples(dominant) versus Right– no dimples (recessive).

Trait (Capital letter – dominant allele) (Lowercase letter– recessive allele) Possible Genotype s Your Phenoty pe Your Genotyp e Widow’s peak – W Straight hairline – w WW, Ww, ww Widow’s peak Ww Earlobes unattached – U Earlobes attached – u UU, Uu, uu Earlobes unattach ed Uu Skin pigmentation: Freckles – F No freckles – f FF. Ff, ff No freckles ff Hair on back of hand – H NO hair on back of hand – h HH, Hh, hh No hair on back of hand hh Dimples – D No Dimples – d DD, Dd,dd No dimples dd Polydactyly (more than 5 fingers) – P Five fingers – p PP ,Pp, pp Five fingers pp Thumb hyperextension – “hitchhiker’s thumb” Last segment cannot be bent backward – T Last segment can be bent backward - t TT, Tt, tt Last segment can’t bent backwar d Tt Questions: 1. What is the homozygous recessive genotype for dimples? What is the phenotype? The homozygous recessive is dd. The phenotype is no dimples. 2. Does an individual with Pp exhibit the symptoms of polydactyly (more than 5 fingers)? Why or why not? Yes, any person with polydactyly has the genotype of Pp, where P represents the allele that causes polydactyly and p presents the normal allele of this gene. 3. What is the genotype for an individual who is heterozygous for hitchhiker’s thumb? Will they exhibit the phenotype for hitchhiker’s thumb? The genotype for someone who is heterozygous for hitchhiker’s thumb is Tt. They will not exhibit the hitchhiker’s thumb phenotype instead they will have a straight thumb.

4. Two people who are heterozygous for earlobes unattached have a child. List the genotypes possible for their children regarding earlobe attachment. Show your work. UU (for earlobes unattached) Uu (for earlobes unattached) Uu (for earlobes unattached) uu (for earlobes attached) 5. Ryann does not have freckles, but both their parent’s do. Deduce the genotype of their parents. What is Ryann’s genotype? The parents genotype are FF and Ff. Ryann’s genotype is ff. 6. Godric is heterozygous for widow’s peak and has no hair on the back of his hand. His partner has a straight hairline and is heterozygous for hair on the back of their hand. a. What is Godric’s genotype? Ww , hh (heterozygous widow’s peak; no hair back of hand) b. What is his partner’s genotype? ww , Hh (straight hairline, heterozygous-hair back of hand) c. What possible genotypes will their children have for hair lines? WW, Ww, ww d. What possible genotypes will their children have for hair on the back of the hand? Hh, hh

Part 2: A Taste of Genetics – Life Example with Taste Every organism on Earth has a different way to perceive the world due to their individual life experiences as well as their genetic make-up. Humans are no different; every individual has their own experiences that shapes their world perception but so too does their DNA. You may be surprised to learn that 99.9% of the human genome is identical from one individual to the next, and it is the 0.1% difference that makes each individual unique. Some of these differences can affect our sensory systems and how we perceive the natural world. For example, over time we have learned which things taste good and are good for us while simultaneously learning which things taste bad or are bad for us. Specifically, bitter compounds are closely associated to toxic substances in nature. The way we know things taste bitter, or any other flavor for that matter, is because we have special chemical receptors in our mouth and nose that bind molecules in our food and send signals to the brain telling it what the food tastes like. Figure 6: A chemical binding a membrane receptor One type of bitter receptor in our mouth senses the presence of a chemical called phenylthiocabamide, or PTC. PTC is a non-toxic chemical, but it very closely resembles toxic compounds often found in food. The unique thing about PTC is that not everyone can taste it! We first learned this in the 1920s when Arthur L. Fox and C. R. Noller were working with PTC powder and Noller complained about the extremely bitter taste while Fox tasted nothing at all. This led to experimentation where scientists ultimately discovered the ability to taste PTC was hereditary; it was in our DNA! The ability to taste PTC comes from the gene TAS2R38 which encodes one of the chemical receptors in our mouth that binds to PTC. By comparing PTC tasters to non-tasters, scientists have found three single nucleotide polymorphisms (SNPs) that differentiate the taster allele (T) from the non- taste allele (t). A SNP is a genetic mutation where one nucleotide in DNA is different from one individual to the next. The word mutation sounds scary, but a mutation is not always bad; there are nearly 10 million SNPs in humans

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